The SRS99 is a semi-automatic, gas-operated rifle that fires 14.5×114mm ammunition from a four-round detachable box magazine. It can be fitted with high power rounds, which, according to Jun-A266, "can take the hat off an Elite at 2,000 yards." The ejection port is on the right side of the weapon and the charging handle is on the left side. Unlike most other known models of the SRS99 series, this variant features a thumbhole stock instead of a pistol grip, and its body sports a black and navy blue finish in addition to the gray of its successors. Also unlike its successors, it can be seen utilizing a sling mount in-game. The SRS99's scope is similar to the SRS99D-S2 AM's scope, as both display green outlines of objects.

The SRS99 proves its worthiness as a long range weapon, capable of picking off single targets with a lethal shot. It can be used to neutralize significant threats that would've been a problem for the player to tackle in CQC. Other than serving as an offensive role, the SRS99 can also be used to 'cheat' on enemies when their emplacements are unknown: its scope is efficient for surveillance, reconnaissance and scouting, allowing the user to relay information back to other teammates so they will be prepared for any surprises that the opposition had rigged. Also, it has an added armor piercing effect making it a deadly force against enemy vehicles. For instance, it take only takes four rounds to completely destroy a Banshee, or three rounds to destroy a Ghost and two rounds to take out a tank; one to eliminate the canopy and a following shot to kill the driver.

The SRS99 is very cumbersome to use in short range combat: the length of its barrel makes it troublesome for users to aim it in tight quarters. A sniper's shot will also give off a white trail of vapor which can be traced back to the shooter's location. Because of this, a sniper's general location can be estimated after very few shots, leaving the shooter the choice of going to a new position or facing the possible counterattack. Ideally, a sniper would move and shoot at the same time, but the narrow field of view in the scope can make the user clumsy and situationally unaware, and the shifting viewpoint makes tracking targets more difficult. When firing, the bullet does not hit its target immediately, the travel time needs to be taken into account when tracking targets at long range. A skillful target will also make scoring headshots difficult: a single hit scored on a sniper will automatically cause the sniper to exit scope mode, so a single grenade can kill the sharpshooter if the enemy aims properly.

In the Halo: Reach Beta the scope shows the identity of its user, SPARTAN-B312, as "ID-NOBLE6," regardless of whoever wields it. There is also a small UNSC logo on the left of the scope. The Noble 6 ID tag has been removed in the final version of the game.

Though the Sniper Rifle features reticle bloom, it only has a very miniscule effect on the weapon, retracting almost to its smallest size before firing. This can be tested by firing the weapon as fast as possible with the "Bottomless Clip" setting turned on. After many consecutive shots, the reticle will reach a point where it is fully bloomed.

The Sniper Rifle is portrayed as a true Anti-Matériel rifle in Halo: Reach; it is now capable of destroying armored vehicles in as few as 4 shots.

The rifle appears to have a rear "notch" type sight, but no front sight. The rear sight also does not appear to be adjustable for elevation or windage, but has markings for windage. This is very strange for a weapon that may need to be used without a scope in some situations, such as if the scope is damaged.

If a hologram is deployed, it will flash in the night vision scope when not zoomed in, as it is turned to normal vision if zoomed in.

The scope, like other weapons, has a compass.

As with the Drop Shield, it is unwise to fire the weapon while walking through a shield door. It will have one of two results, resulting in either shield damage or instant death. If fired at a certain angle, you can kill yourself with a headshot.

The rifle's rounds ricochet off walls if they hit at a shallow angle, and still deal damage when they do so.